Another spur question

[Mike S]

I want to take a spur from a socket in my kitchen to supply a new double socket. However the socket from which I want to take the spur is itself supplied from an independent unfused switch which itself acts as a sort of junction box in the ring main. The existing socket supplies the fridge/freezer and that alone and is located in an inaccessible position behind the fridge/freezer - hence the separate switch. The new socket will be used to power a TV and stereo and nothing else.

Can anyone tell me whether this is a) dangerous, and b) legal?

I know you are not supposed to 'take a spur from a spur'. However, would this fall into that category, since the first spur is not from a socket but from a switch (which as I said is not fused)?


Thanks for any advice anyone can give me on this.

Mike

 

[PrinceofDarkness]

It would be neither dangerous or 'illegal' to extend that circuit in that way. It might contravene a non-statutory 'rule', in which case you could set your mind at rest by replacing that unfused switch with a 13A FCU.....


Lucia.

 

[PrinceofDarkness]

Then again: One of the 'Part-P' crusaders might have something to say.

 

[ban-all-sheds]

However the socket from which I want to take the spur is itself supplied from an independent unfused switch which itself acts as a sort of junction box in the ring main.

What is the rating of that switch?

What is the rating of the circuit?

Is it a ring or a radial?

What size cable is the main circuit, and what size is the spur?

The new socket will be used to power a TV and stereo and nothing else.

Doesn't matter - a socket is a socket.

Can anyone tell me whether this is a) dangerous, and b) legal?

Possibly, and therefore possibly not.

I know you are not supposed to 'take a spur from a spur'. However, would this fall into that category, since the first spur is not from a socket but from a switch (which as I said is not fused)?

Yes it would, if this is a ring. A spur doesn't have to originate from a socket - it can come from anywhere.

Thanks for any advice anyone can give me on this.

You should also read this:

//www.diynot.com/wiki/electrics:part-p

 

[PrinceofDarkness]

Oh yes! Be sure to read "electrics: part_p". It's so vitally important......

Not.



Lucia.

 

[Mike S]

It would be neither dangerous or 'illegal' to extend that circuit in that way. It might contravene a non-statutory 'rule', in which case you could set your mind at rest by replacing that unfused switch with a 13A FCU.....

Thanks Lucia for this and suggestion about 13A FCU.

 

[Mike S]

What is the rating of that switch?

What is the rating of the circuit?

Is it a ring or a radial?

What size cable is the main circuit, and what size is the spur?

The circuit itself is dedicated to the kitchen and protected by 32A circuit breaker in the CU. I'm assuming it is a ring circuit, but in truth it's just an assumption based upon the fact that the property is a relatively modern property built in early 1990s with all electrics as originally installed with no DIY or other subsequent work.

The property is a very small terrace house with the kitchen circuit (that I want to draw up) supplying just two double sockets plus a separate washing machine socket plus the socket for the fridge/freezer. I want to use the latter socket to create the new socket for a TV in a corner in the living area just behind the kitchen dry-wall. I thought this might be safer and certainly less unsightly than a flex extension cable from an existing socket in the kitchen or living area.

Thanks for you time and attention.

Mike

 

[Mike S]

What is the rating of that switch?

What is the rating of the circuit?

Is it a ring or a radial?

What size cable is the main circuit, and what size is the spur?

I'm wondering now whether perhaps it is a radial since it seems to be 4mm cable protected by 32 amp circuit breaker covering only a very small property? Does that mean any spurs should use 4mm cable too? I guess if I spurred with 2.5 mm 23amp rated cable, then I would need some extra protection for that spur such as 13amp FCU?

 

[ban-all-sheds]

It would be neither dangerous or 'illegal' to extend that circuit in that way. It might contravene a non-statutory 'rule', in which case you could set your mind at rest by replacing that unfused switch with a 13A FCU.....

Thanks Lucia for this and suggestion about 13A FCU.

Mike - you should ignore most of that advice, it is incorrect.

It MIGHT be dangerous to extend the spur as it is, and if it is dangerous it WILL BE illegal.

The Building Regulations, which are an actual law, mandate that reasonable provision shall be made in the design and installation of electrical installations in order to protect persons operating, maintaining or altering the installations from fire or injury.

So doing something dangerous is not going to count as reasonable provision to protect persons operating, maintaining or altering the installations from fire or injury, and therefore will be illegal.

Changing the switch for an FCU fused at 13A is not a "setting your mind at rest" - it's what you must do if you cannot determine what cable sizes and circuit type and rating is being used. Not to do so would not be reasonable.

Adding the new socket without notification is also illegal, but not dangerous.

There is the issue of testing the new socket , and whether it should be considered reasonable to expect it to be tested or not.

The circuit itself is dedicated to the kitchen and protected by 32A circuit breaker in the CU. I'm assuming it is a ring circuit, but in truth it's just an assumption based upon the fact that the property is a relatively modern property built in early 1990s with all electrics as originally installed with no DIY or other subsequent work.

You should not assume.

I want to use the latter socket to create the new socket for a TV in a corner in the living area just behind the kitchen dry-wall. I thought this might be safer and certainly less unsightly than a flex extension cable from an existing socket in the kitchen or living area.

Don't forget the rules for concealed cables.

• http://www.voltimum.co.uk/files/gb/attachments/niu/l/attachments/c5-43.pdf
• http://web.archive.org/web/20061110111450/http://www.niceic.org.uk/downloads/concealedcables.pdf
• IEE article
• IEE Article on 17th Edition requirements for concealed cables.

Is the socket circuit RCD protected?

 

[ban-all-sheds]

I'm wondering now whether perhaps it is a radial since it seems to be 4mm cable protected by 32 amp circuit breaker covering only a very small property?

How did you measure the size of the cable?

How many conductors are there in the MCB for that circuit, and does it all stop working when you turn the MCB off?

Does that mean any spurs should use 4mm cable too?

Yes, if you don't use an FCU.

That switch had better be rated at 32A too.

I guess if I spurred with 2.5 mm 23amp rated cable, then I would need some extra protection for that spur such as 13amp FCU?

2.5mm² isn't always rated at 23A, but it'll be OK on a 13A fuse.

 

[Mike S]

You should not assume. ....

Is the socket circuit RCD protected?

Thanks, yes, I take your point about not assuming!

Yes, socket circuit is RCD protected

 

[Mike S]

How did you measure the size of the cable?.....

How many conductors are there in the MCB for that circuit, and does it all stop working when you turn the MCB off?...

That switch had better be rated at 32A too......

.....2.5mm² isn't always rated at 23A, but it'll be OK on a 13A fuse.

I didn't measure the size of the cable... may latest assumption (sorry!) was based on a diagram located at a well-known DIY store that suggested that 4mm ring circuits are protected by 32A MCBs and 2.5mm circuits by 23 amp. Since my circuit is protected by 32A MCB I thought that maybe.... anyway I take your point about the dangers of making assumptions.

I don't know how many conductors there on the MCB as I haven't yet had the nerve to open that up to look. But yes when I turn off the MCB all the
sockets connected to the kitchen circuit are deactivated.

The switch was installed at the time the house was built and wired so I would like to think that they connected an appropriately rated switch.

Anyway, from what I gather my best bet is too replace the existing switch with a 13A FCU.

What I'm curious about, though, is the nature of the risk. Is it above all that a spur with a lower rating than the main circuit will get overloaded and cause a fire before the 32A MCB kicks in? Presumably the fuses in the plugs for the appliances connected to the spurred socket would blow if anything went wrong that side of the socket, or might that be too slow to prevent overloading in the spur itself?

Thanks again for your advice.

Mike

 

[ban-all-sheds]

I didn't measure the size of the cable... may latest assumption (sorry!) was based on a diagram located at a well-known DIY store that suggested that 4mm ring circuits are protected by 32A MCBs

That's b******s.

and 2.5mm circuits by 23 amp.

So is that.

The switch was installed at the time the house was built and wired so I would like to think that they connected an appropriately rated switch.

I'm sure you would.

But that would be another assumption.

Anyway, from what I gather my best bet is too replace the existing switch with a 13A FCU.

TBH your best bet would be to get an electrician.

What I'm curious about, though, is the nature of the risk. Is it above all that a spur with a lower rating than the main circuit will get overloaded and cause a fire before the 32A MCB kicks in?

Yup.

Presumably the fuses in the plugs for the appliances connected to the spurred socket would blow if anything went wrong that side of the socket, or might that be too slow to prevent overloading in the spur itself?

The fuse in a plug will prevent a single socket from overloading a spur cable, which is why you're allowed an unfused spur with one socket on it even if the cable isn't rated for the circuit protective device.

A fault on the spur cable would be taken care of by the circuit protective device, but an overload caused by multiple sockets wouldn't be.

 

[Mike S]

TBH your best bet would be to get an electrician.

I may well do that, but I will still want to know what he is doing and why he's doing it... otherwise I will once again just have to "assume" that he has done a proper job!

I made that assumption once with a shower and boiler installation which was done by fully qualified, corgi registered etc, plumber and heating engineer... It all worked OK and still does, but a different plumber/engineer subsequently told me that both the shower and pump for the central heating had been connected up incorrectly... at least not according to the regs and best practice. So now when I need work done in the home I either do it myself or at least try and understand how it should be done and why it should be done that way before I pay someone else to do it.

Anyway I'm grateful for all the information I've picked up here, so thanks again. I'm amazed at the patience professionals here (like yourself perhaps) have with some of us DIY folk!

 

[Risteard]

Does that mean any spurs should use 4mm cable too?

Yes, if you don't use an FCU.

That switch had better be rated at 32A too.

Ignoring the fact that this appears to be a 2.5mm² ring final circuit as opposed to a 4mm² radial final circuit, why do you contend that it is non-compliant to have an unfused spur off a 4mm² radial final circuit in 2.5mm² cable?